SMALL Flexible Reverse Osmosis System for Off-GRID Water Purification and Desalination

small Flexible REVERSE OSMOSIS SYSTEM for off-grid Water Purification and Deslaination  

Authors:      Tae Lee^#, Anditya Rahardianto, Yoram Cohen

                        Chemical and Biomolecular Engineering Department and Institute of the Environment and Sustainability, Water Technology Research Center, University of California Los Angeles,

  Abstract

Various remote communities around the world are confronted with impaired local water supplies. In such communities establishing and maintaining reliable distributed water treatment systems for the production of safe drinking water is a major challenge. Water treatment systems for deployment in remote communities must possess the following attributes: a) provide a physical barrier for reliable contaminant removal, b) high operational flexibility to handle geographical and temporal variability of feed water quality and other operational requirements (e.g., water recovery), c) amenable to process automation, d) compact foot-print capable for fixed or mobile deployment, and e) standardized system configuration (for ease of maintenance and operator training). In this regard, membrane-based (nanofiltration (NF) and low-pressure reverse osmosis (RO)) water treatment is most suitable for meeting the above needs. Accordingly, a novel flexible RO/NF (FRO) system platform was developed with enhanced small-system energy efficiency and high operational flexibility (allowing a wide water recovery range of 10-95%), while minimizing plant footprint. Advanced system control was implemented that enables autonomous, self-adaptive operation of FRO over a wider range of feed water salinity (e.g., 500 mg/L – 35,000 mg/L) while maintaining energy-optimal conditions. A key feature of FRO is the ability to switch (on demand) between various operational modes (e.g. batch, continuous, and semi-batch modes) depending on feed water conditions and treatment targets using a single system platform. Furthermore, the present unique FRO system design enables continuous operation (without interruptions of permeate productivity) and without the need for a typical high pressure pump (>150 psi) used in single or multi-stage RO systems. System performance was then analyzed via process models that were validated with both laboratory and field data for brackish water and sea water desalination, as well as for nitrate removal from impaired potable groundwater sources. Both experimental and modeling results demonstrated that the innovative FRO system platform allows for flexible operation over a wide range of product water recovery, while maintaining high energy efficiency (i.e., low energy consumption suitable for use with renewable energy). Therefore, FRO is particularly attractive for distributed deployment in rural or isolated communities where high water recovery is critical for various water sources of different salinity levels.